Using premium CI features like 'trigger' in gitlab-ce gives extremely misleading error messages

Summary

Using a feature like trigger in a .gitlab-ci.yml file on a gitlab-ce deploy gives this error message on pipelines or when validating the file:

root config contains unknown keys: <jobname>

when the actual problem is the use of unsupported config inside the job itself. This can be observed in-the-wild at https://dev.gitlab.org/gitlab/www-gitlab-com/pipelines/133083 for example (where dev.gitlab.org is a gitlab-ce deploy, and the repo is mirrored from the main repo on gitlab.com which is a gitlab-ee Ultimate deploy).

Steps to reproduce

• Install gitlab-ce
• Create .gitlab-ci.yml with a job that contains the 'trigger' key/option.

Example Project

https://dev.gitlab.org/gitlab/www-gitlab-com/

What is the current bug behavior?

Error message is:

root config contains unknown keys: <jobname>

What is the expected correct behavior?

An error message that points to the fact that trigger (or whatever other higher-license feature is in use) is not available for use because of licensing.

Relevant logs and/or screenshots

https://dev.gitlab.org/gitlab/www-gitlab-com/pipelines/13308 gitlab-ce 12.3.5+rnightly.133065.96dd7daf-0